Internalization and thermal susceptibility of Shiga toxin-producing Escherichia coli (STEC) and internalization and antimicrobial susceptibility of Salmonella Typhimurium in marinated beef products under simulated industrial conditions
MetadataShow full item record
Marinated meat products hold a significant portion of the retail and foodservice meat industry. The internalization and survivability after cooking of Shiga toxin-producing Escherichia coli (STEC) serogroups in these products is a concern for beef processors and the consumer. We addressed these concerns in this dissertation in two separate studies. One of our studies evaluated the internalization and cooking susceptibility of seven individual STEC serogroups considered adulterants in non-intact meat products (O157:H7, O26, O45, O103, O111, O121, and O145) in marinated beef sirloin steaks. Beef bottom sirloin flaps (IMPS #185A; USDA Select) were inoculated (106 log CFU/cm2) with a multi-strain cocktail of individual serogroups (seven total) prior to vacuum tumbled marination (30 or 60 min) and storage (14 d). After storage, flaps were cooked to various endpoint temperatures (55, 60, 65, and 71°C) for evaluation of pathogen survival by direct plating on MacConkey agar with tryptic soy agar overlay. Pathogen presence after marination, storage, and cooking was determined by direct plating or rapid PCR based detection (BAX®) when numbers were below the enumeration limit. The data indicate varied internalization, translocation, and heat susceptibility patterns among the evaluated STEC serogroups. Sirloin flap sections inoculated with –STEC O145 and marinated for 60 min had more internalized STEC (P< 0.05) than sections marinated for 30 min. However, after storage, internalized STEC populations did not differ (P > 0.05) in sections marinated for 30 min versus those marinated for 60 min. Escherichia coli serogroups O26, O103, and O111 were detected in flaps cooked to 55 and 60°C, while E. coli O157:H7 survived in flap sections cooked to 60 and 65°C. However, STEC O145 was the only serogroup with confirmed pathogen survivability at all cooking temperatures (55, 60, 65, and 71°C). The other two serogroups (STEC O121 and O45) were not detected in any cooked products. In our second study we evaluated Salmonella survival in the products. As the incidence of multidrug resistance (MDR) Salmonella enterica serotype Typhimurium is increasing, data regarding the antimicrobial interventions and pathogen internalization in marinated meat products is important. Our second study evaluated the antimicrobial interventions and internalization of Salmonella Typhimurium in marinated beef sirloin steaks. Beef bottom sirloin flaps (IMPS #185A; USDA Select) inoculated (108 log CFU/cm2) with Salmonella Typhimurium were sprayed (lactic acid (4%) and buffered vinegar (2%)) prior to vacuum tumbled marination (0.35% sodium chloride and 0.45% sodium tripolyphosphate) for 30 min. Pathogen presence after antimicrobial spray, vacuum tumbled marination, and translocation was determined by direct plating on Xylose Lysine Deoxycholate (XLD) agar with tryptic soy agar (TSA) overlay. The data indicated varied internalization and antimicrobial susceptibility pattern of Salmonella Typhimurium in marinated meat. Salmonella Typhimurium was reduced by 2.4 log10 CFU/cm2 in post-inoculated surface attachment. Lactic acid (4%) spray (P <0.0001) and buffered vinegar (2%; P <0.0001) reduced surface populations of Salmonella Typhimurium on inoculated beef sirloin flaps prior to vacuum marination. However, reductions in surface populations were greater (~ 2 log10 CFU/cm2) for lactic acid in comparison with buffered vinegar (P <0.0001). Alternatively, the translocation of Salmonella Typhimurium following vacuum marination was not influenced (P <0.333) by the application of a surface organic acid spray prior to marination. Both of these studies emphasize the importance of considering food safety hazards that can be associated with vacuum marinated meat. Similarly, these data confirm the efficacy and utility of interventions prior to vacuum tumbled marination. Additionally, although surface interventions are efficacious, these data suggest that further research is needed to identify additional strategies to mitigate internalization and translocation of STEC and salmonella Typhimurium into vacuum-marinated meat products.